[PATCH 9/9] docs/style: call out the use of GUARD macros

["Alex Bennée" <alex.bennee@linaro.org>]

There use makes our code safer so we should mention them.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 docs/devel/style.rst | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/docs/devel/style.rst b/docs/devel/style.rst
index 0bd01f3fca..b50a981a86 100644
--- a/docs/devel/style.rst
+++ b/docs/devel/style.rst
@@ -657,6 +657,42 @@ that declaration and the new code.
 
 See :ref:`qom` for more details.
 
+QEMU GUARD macros
+=================
+
+QEMU provides a number of ``_GUARD`` macros intended to make the
+handling of multiple exit paths easier. For example using
+``QEMU_LOCK_GUARD`` to take a lock will ensure the lock is released on
+exit from the function.
+
+.. code-block:: c
+
+    static int my_critical_function(SomeState *s, void *data)
+    {
+        QEMU_LOCK_GUARD(&s->lock);
+        do_thing1(data);
+        if (check_state2(data)) {
+            return -1;
+        }
+        do_thing3(data);
+        return 0;
+    }
+
+will ensure s->lock is released however the function is exited. There
+are often ``WITH_`` forms of macros which more easily wrap around a
+block inside a function.
+
+.. code-block:: c
+
+    WITH_RCU_READ_LOCK_GUARD() {
+        QTAILQ_FOREACH_RCU(kid, &bus->children, sibling) {
+            err = do_the_thing(kid->child);
+            if (err < 0) {
+                return err;
+            }
+        }
+    }
+
 Error handling and reporting
 ============================
 
-- 
2.39.2